1. Field of the Invention
The present invention relates generally to implantable medical devices, and more particularly, to a power link for implantable medical devices.
2. Related Art
Many implantable devices have a transcutaneous link to provide continuous or intermittent transfer of electrical power to the implanted device, often from an externally worn battery. The most common form of such a power link uses, two magnetically coupled air coils, typically operating at a frequency in the megahertz range, with the power supplied from an external battery source.
Some implants are constructed from non-conductive materials, for example ceramics, and in this case the implanted coil may be positioned inside the casing. Other implanted devices are housed in metal enclosures, for example formed from titanium or alloys thereof. Titanium is widely used for medical implants since it is inert within the human body, lightweight and strong. Active implantable medical devices (AIMD) such as cochlear implants (Cl) generally have reinforced titanium casings.
When an inductive link is arranged to operate across a casing made of titanium or other conductive material, the casing generally operates to shield the incoming power and absorb it, causing an increase of temperature of the casing and hence the contained device. Accordingly, for such devices the implanted air coils have been typically embedded in a flexible biocompatible and electro-magnetically transparent material (e.g. polymers, silicone rubbers), and located external to the casing. As a consequence of improvements in battery technology, the current trend is for implantable devices to include battery capacity, to allow for periods of operation without access to an external power source. This allows for the possibility of totally implanted devices, with clear aesthetic and practical advantages for the users.